IBM8FD.WS4 (=IBM 8" Floppy Diskette)
----------
"The IBM Diskette General Information Manual"
IBM Document GA21-9182-4
Fifth Edition: August 1979
(Retyped by Emmanuel ROCHE. Posted to comp.os.cpm.amethyst by Roche
on 26 May 2006.)
Preface
-------
This publication is intended for use by anyone who uses IBM
diskettes, or who is interested in learning about or using them.
You are not required to have any prior knowledge of diskettes,
but you are expected to have a basic knowledge of data
processing. To help you learn about IBM diskettes, this
publication provides:
- General information about the advantages of diskettes,
their uses, and their physical appearance.
- Some suggestions for handling and replacing diskettes.
- Some basic information about the location and addressing
of the data on the diskette.
- Detailed information about the systems and devices that
use IBM diskettes and how the diskettes are organized.
In this manual, the term system or IBM system includes those
devices that use diskettes but are not, by definition, systems.
Related publications
--------------------
This publication is designed to present general information
about IBM diskettes. For more specific information about the way
diskettes are used in individual systems, refer to the
appropriate system documentation. Generally, diskette
information appears in publications such as:
- Operator's guides
- System summaries
- Functions reference manuals
- System introductions
- Component descriptions
- Customer setup manuals
Contents
--------
INTRODUCTION
The IBM diskette
The advantages of diskettes
The purposes for diskettes
THE PHYSICAL FEATURES OF DISKETTES
The protective envelope
The identifying and operating features
The identifying features
The operating features
The diskette drive
DISKETTE HANDLING
Conserving information
Inserting diskettes
Removing diskettes
Labeling diskettes
Storing diskettes
Environmental requirements
Diskette magazine storage
Short-term storage
Long-term storage
Shipping diskettes
REPLACING DISKETTES
Damaged diskettes
Worn diskettes
Suggestions for diskette operations
DISKETTE ADDRESSING AND LAYOUT
The track
The cylinder
The head
The sector
The address
The index cylinder
Alternative cylinders
IBM DISKETTE TYPES
IBM diskette 1
128 bytes per sector
256 bytes per sector
512 bytes per sector
IBM diskette 2
128 bytes per sector
256 bytes per sector
IBM diskette 2D
256 bytes per sector
512 bytes per sector
1024 bytes per sector
ACCESSORIES, DISKETTES, AND SUPPLIES
APPENDIX A. DISKETTE USERS
IBM diskette 1
IBM diskette 2
IBM diskette 2D
APPENDIX B. DATA ORGANIZATION
Physical and logical records
Blocking and spanning
Sequential data
APPENDIX C. INITIALIZATION AND TRACK FORMAT
Initialization
Track format
APPENDIX D. INDEX CYLINDER LAYOUT
APPENDIX E. DATA SET LABEL LAYOUT
APPENDIX F. DATA EXCHANGE
Basic data exchange
Type H data exchange
Type E general exchange
APPENDIX G. GLOSSARY
INDEX
INTRODUCTION
------------
The IBM diskette
----------------
The IBM diskette is a small, convenient, storage medium for use
on various data processing systems and devices. The IBM diskette
is composed of two parts: the semirigid plastic jacket that
protects the disk, and, sealed inside the jacket, a thin,
flexible disk that turns freely inside the jacket. The disk,
coated with a magnetic material, provides the recording surfaces
of the diskette. These surfaces are kept clean by a low-friction
liner in the jacket.
The diskette is ordinarily used singly. However, there are IBM
systems that use diskettes enclosed in containers that can hold
up to 10 diskettes. These containers are called magazines. When
it is used in a system, the entire magazine slides into the
diskette drive. (A diskette drive is the device that reads from
or writes on diskettes.)
The advantages of diskettes
---------------------------
For years, the primary permanent storage device in data
processing was the punched card. Eventually, however, storing
the great quantities of punched cards needed to maintain an
active system became a burden. The diskette provides one
solution to the storage problem, but there are other advantages
in using diskettes:
- Diskettes can contain more information than cards.
The amount of information that can be stored on
individual diskettes is many times greater than the
amount of information that can be stored on individual
cards.
- Diskettes can be rewritten many times; cards can be
completely punched only once.
Diskettes can be reused to store new information after
the information they contain is no longer needed. Cards
cannot be punched a second time; once the information
they contain is obsolete, the cards must be stored or
thrown away.
- Diskettes can be corrected, but the information on cards
cannot be changed.
Incorrect data on diskettes can be corrected by placing
the correct information in the locations containing
incorrect information. This is a simple rewriting
process. Because holes are punched in cards to store
information, new cards must be punched to correct
errors.
- Diskettes are easier to handle than cards.
The information stored on diskettes can be more easily
moved, stored, and mailed than the same amount of
information stored on cards.
The purposes for diskettes
--------------------------
Diskettes can be used as storage media for various kinds of
information. The particular purpose for the diskette varies with
the application for which the diskette is used in any particular
system. Because of these variations, this manual makes no
attempt to list every possible use for diskettes, but among the
more standard uses are:
- Storing data for exchange between devices or systems
- Saving system data, offline, to be restored to the
system at a later time as needed
- Logging or buffering transaction data for batch processing
- Processing system data (usually in small systems or in
control units)
- Storing and loading system microcode
- Distributing programs
- Storing and loading diagnostic information
Some systems and devices have diskette drives that are not
accessible to the operator. The diskettes in these drives
usually contain microcode or diagnostic information for use in
the particular systems or devices.
Because the uses for diskettes vary from system to system, IBM
produces diskettes of varying types and capacities. Briefly,
there are three basic types of diskettes, they are:
- IBM diskette 1. This diskette contains information on
one side only.
- IBM diskette 2. This diskette contains information on
both sides.
- IBM diskette 2D. This diskette contains information
written in double-density encoding (twice the standard
number of bits written on a given track) on both sides.
A complete description of the diskettes is provided under
"Diskette types", later in this manual.
THE PHYSICAL FEATURES OF DISKETTES
----------------------------------
Physical features are those characteristics that make any object
consistently recognizable. The protective envelope and all the
various labels, holes, slots, notches, and dimensions form the
physical features of the IBM diskette.
The protective envelope
-----------------------
The protective envelope is an essential part of all IBM
diskettes, even though you must remove the envelope before you
can put the diskette in the diskette drive. The object of
protecting a diskette is to protect the information contained on
that diskette.
Except when it is in the diskette drive or a magazine, the
diskette should always be in its protective envelope.
An unprotected diskette is stored information that is
vulnerable. The information is subject to unknown alteration or
destruction from many sources. Some examples of things that can
damage diskettes that have been left out of their protective
envelope are: fingerprints, smoke, sneezes, spilled drinks,
coughs, dust, and ashes. (Diskette damage is discussed in detail
under "Diskette handling", later in this manual.)
The identifying and operating features
--------------------------------------
The remaining features are part of the diskette itself. The
identifying features are for your use while the diskette is
outside the diskette drive, and are visible when the diskette is
in its protective envelope. The operating features are those
features that allow the diskette to be read from or written upon
while it is inside the diskette drive.
The identifying features
------------------------
There are diskette labels on which you can record the
descriptive, operational, and historical information that you
want to remain with the diskette. Further information on the
labels is provided under "Labeling diskettes" later in this
manual.
1. Permanent diskette label (Square label at upper left
corner)
Use this label to record information describing the
diskette and its condition. Record information such as:
- The serial number (volume ID; see Appendix D)
- The date you first used the diskette
- The location of any defective cylinders
2. Temporary identification label (Horizontal label at top)
Use this adhesive label to record changing items such as:
- The data stored on the diskette; job numbers, names,
and dates
- The identification of the person who entered the
information
- The date of data verification
- The device used to write the information on the diskette
The operating features
----------------------
Each of these features contributes in some way to the operation
of the diskette when it is in the diskette drive. The operating
features are holes in the diskette jacket, and two of the holes
extend through the disk that is sealed inside the tacket.
1. Index hole
There is an index hole that passes completely through
the diskette. When the diskette is in the diskette
drive, the disk turns inside the jacket. Once per
revolution, the holes in the disk and the jacket line up
and allow a beam of light to shine through the index
hole. The light beam is used for a number of purposes,
some of which are:
- Timing for various functions within the diskette drive
- Verifying that the diskette is of the correct type for
the diskette drive
- Verifying that the diskette is properly installed in
the diskette drive
- Providing timing and synchronizing for communications
between the system or device and the diskette drive
The index holes on one-sided and two-sided diskettes do
not occupy the same location on the diskette. The index
hole is centered (at 12 o'clock) on one-sided diskettes,
and is offset to the right (at 1 o'clock) on two-sided
diskettes.
2. Drive spindle hole
The diskette drive spindle requires that there be a hole
in both the diskette jacket and the disk inside the
jacket. When the diskette is seated in the diskette
drive, the drive spindle moves into the drive spindle
hole and clamps to the disk, causing the disk to begin
turning.
3. Head slot
The head slot exposes the recording surface of the
diskette to the read/write head. There is a head slot on
both sides of each type of diskette. On a one-sided
diskette, a pressure pad enters the head slot opposite
the read/write head. On a two-sided diskette, data is
recorded on both sides of the diskette, so a read/write
head enters both head slots.
4. Stress relief notches
The stress relief notches in the diskette jacket aid in
distributing the stresses that occur in the head slot
area if the diskette is accidentally bent.
The diskette drive
------------------
The diskette drive provides the means for reading or writing on
the diskette. Under control of the system, the diskette drive
transfers encoded information to or from the diskette by using
an electromagnetic read/write head. The drive moves the
read/write head into position on the moving recording surface of
the diskette, and writes magnetically charged spots (small
magnetic fields) at specific locations (addresses) on the
recording surface. The information written at an address remains
there until it has been replaced by new information, or is
magnetically erased.
To read from the diskette, the diskette drive moves the
read/write head to the proper position on the diskette recording
surface, finds the proper address, and senses and transmits the
information to the system.
Because there are diskettes that can store information on both
sides, some diskette drives have two read/write heads, one on
each side of the diskette.
DISKETTE HANDLING
-----------------
IBM diskettes are designed to withstand the stresses of normal
and frequent handling. However, there are some precautions that
you should note as you handle your diskettes. By careful
observance of these precautions, and guarding against
carelessness in everyday use, your diskettes will provide long
and reliable service.
The proper way to remove a diskette from its protective envelope
is to grasp the diskette by its upper edge, and pull it out of
the envelope.
Be sure to keep the protective envelope and return the diskette
to the envelope every time you remove the diskette from the
diskette drive. As its name implies, the protective envelope is
provided to help prevent damage to the diskette. The damage on a
diskette can cause problems that range from intermittent reading
or writing errors to a permanent loss of the information
contained on the diskette.
Conserving information
----------------------
When a diskette is damaged or mishandled, the information
contained on that diskette can be lost or altered. The following
paragraphs point out some of the more common handling mistakes.
These mistakes are almost always the result of a moment's
carelessness. Diskettes are not, in themselves, highly
expensive; but the information they contain can be very costly
if it is lost.
Diskettes can be damaged in many ways. They can be bent,
creased, warped, dented, contaminated, or magnetically altered.
Bent diskettes
IBM diskettes are made to be flexible, but the flexibility is to
allow the diskette to function more freely in the diskette
drive. Diskettes should not be grasped too vigorously,
especially near the head slot, nor should paper clips or rubber
bands be placed on them. The bending caused by any of these
actions can be permanent.
Creased diskettes
Folding a diskette or placing heavy objects on it can cause it
to be creased. A crease is permanent, and ruins the diskette.
Warped diskettes
Warping is usually the result of exposing the diskette to
temperatures above the safe limit (see "Environmental
requirements", later in this chapter). However, there are other
causes for warping also. A diskette that is held in a bent
position for too long will warp. Improper storing can also cause
diskettes to warp. A diskette that is warped will never return
to its original shape.
Dented diskettes
You should use a fiber-tip pen to mark on diskette labels.
Pressure from a ball point pen might cause dents in the
recording surface. Dents result in lost information because the
read/write head loses contact with the recording surface.
Pencils are not recommended because they are erasable. You
should never erase on a diskette because the eraser dust can get
inside the diskette jacket and contaminate the recording
surface. Contamination is discussed in the next paragraph.
Contaminated diskettes
A diskette is damaged by contamination when the recording
surface is touched, spotted, or dampened by an oily, sticky,
magnetic, abrasive, or, in some cases, a non-abrasive substance.
Examples of these substances are:
- Fingerprints or smoke (oily)
- Soft drinks or coffee (sticky)
- Ferrous dust or filings (magnetic)
- Dust or filings (abrasive)
- Pencil eraser dust (non-abrasive)
Magnetically altered diskettes
Do not place magnets or magnetized objects near the diskette.
The magnetic field produced by these magnets can effectively
erase information from the surface of the diskette. The diskette
does not suffer any physical damage, but the information it
contains may no longer be accurate.
Inserting diskettes
-------------------
The method by which the diskette is locked into the diskette
drive varies with the type of diskette drive you have. There
are, however, some general statements that should be made about
diskette insertion. Always exercise care in placing a diskette
in a diskette drive or in a diskette magazine. Be sure you:
1. Carefully remove the diskette from its protective
envelope. Be careful not to touch any of the exposed
areas of the recording surface.
2. Without bending the diskette, slowly push the diskette
into the diskette drive or magazine until it stops.
3. Slowly close the diskette drive cover or move the
diskette locking lever.
Removing diskettes
------------------
Always exercise care when removing a diskette from a diskette
drive or a diskette magazine. Depending on the type of diskette
drive you have, be sure you:
1. Completely open the diskette drive cover, move the
diskette locking lever as far as it will go, or lower
the diskette magazine retaining spring.
2. Without bending the diskette, slowly pull the diskette
completely clear of the diskette drive or magazine. Be
careful not to touch any of the exposed areas of the
recording surface.
3. Carefully put the diskette back into its protective
envelope.
Labeling diskettes
------------------
There are two labels provided for each diskette. The permanent
labels are already attached to the diskette jackets, and the
temporary labels come in a packet with each order of 10
diskettes. The temporary labels come in five different colors:
red, blue, green, yellow, and gray. The colors allow you to
identify the various types of information without having to read
the labels. A description of the two labels, and some examples
of the kinds of entries you could make on them, is provided
under "The physical features of diskettes", earlier in this
manual.
As discussed under "Diskette handling", earlier in this manual,
a fiber-tip pen is the only recommended writing instrument for
marking on the diskette labels. Always have the diskette in its
protective envelope when you are writing on the labels; your
hand or wrist could accidentally contact and contaminate the
recording surface. The envelope is cut away to permit you to
write on either label.
When starting a new job on a diskette, cross out, rather than
erase, the old information on the label (the dust from the
erasure can get inside the diskette jacket and contaminate the
recording surface). When the label is full, remove it and attach
a new one. Do not put new labels over old ones, because the
label buildup can affect the performance of the diskette drive.
Do not attach labels to the reverse side of the jacket, and do
not cover any of the holes.
Replace the temporary labels every 6 months, even of they are
not filled. Otherwise, the adhesive can harden and make the
label difficult to remove.
If you wish, you can attach the temporary labels to the
protective envelope, instead of the diskette jacket. Write the
diskette serial number on the envelope and on the permanent
label, to ensure that you will always return the diskette to the
correct envelope.
Storing diskettes
-----------------
Environmental requirements
--------------------------
Temperature: 10 degrees C to 51 degrees C (50 degrees F to 125
degrees F)
Relative humidity: 8% to 80%
Maximum wet bulb temperature: 29 degrees C (85 degrees F)
CAUTION
If a diskette has been stored in an area in which the
temperature is markedly different from the operating temperature
of the diskette drive, do the following:
1. Remove the diskette from its shipping container.
2. Wait 5 minutes for the diskette to adjust to the
operating temperature of the diskette drive. You must
wait longer if you are using a diskette magazine,
because the diskettes are closely packed in the
magazine, and will change temperature more slowly.
Diskette magazine storage
Store diskette magazines so they stand vertically. If the
magazines contain diskettes, be sure to put the lid on the
magazine to lock the diskettes in position and inhibit warping.
Short-term storage
You may store diskettes flat in their envelopes, in stacks of 10
or less, when you need the diskettes for immediate use. If you
store the diskettes vertically, support them so they do not lean
or sag.
Long-term storage
If you do not need the diskettes immediately, you may store them
in their original shipping cartons, with each diskette in its
protective envelope. Shipping cartons can be stored either
vertically or horizontally.
Note: Do not apply pressure to diskette envelopes or cartons,
because pressure can warp the diskettes.
Shipping diskettes
------------------
When shipping a diskette, always label the package "DO NOT
EXPOSE TO HEAT OR SUNLIGHT". When receiving a diskette, check
the carton and the diskette for possible damage. Diskettes can
be safely exposed to temperatures from -40 degrees C (-40
degrees F) to 51 degrees C (125 degrees F) during shipment.
See "Diskettes, supplies, and accessories" for a list of the
shipping and packing materials available from your IBM IRD
(Information Records Division) representative.
To pack one diskette:
- Place the diskette in its protective envelope.
- Put the envelope in a single-diskette carton.
To pack multiples of 10 diskettes:
- Place each diskette in its protective envelope.
- Put 10 diskettes in a 10-pack.
- Put each 10-pack between spacers, to prevent damage
during shipping.
- Insert top and bottom pads in the carton.
- Place the 10-packs and their spacers in the appropriate
sized carton.
CAUTION
Do not use so much filler that the diskettes are tightly
compressed; compression can warp the diskettes.
- Fill the open space in partially filled cartons and 10-
packs with a filler that cannot contaminate the diskette
or enter the diskette jacket.
REPLACING DISKETTES
-------------------
You can prevent most problems from occurring by periodically
examining your diskettes, handling them carefully (see "Diskette
handling", earlier in this manual), and replacing them when
necessary. This chapter offers some things you should look for
and some suggestions that might help you know when replacement
is needed.
Damaged diskettes
-----------------
You should replace diskettes that are:
- Folded
- Creased
- Warped
- Dented
- Contaminated
- Scratched
You may be able to recover the information from a diskette that
has not been folded or warped if the damage is not too severe.
The disk must be free to turn inside the diskette jacket in
order to recover the information. After you have recovered the
information from the diskette, however, discard the damaged
diskette.
Carefully examine any diskette that you suspect may have been
exposed to excessively high temperatures.
You may be able to detect dents by turning the disk inside the
diskette jacket and carefully examining the recording surface.
Note: If you try to turn the disk inside the diskette jacket, be
very careful not to touch any portion of the recording surface.
Any fingerprints on that surface contaminate the surface and
ruin the diskette.
If you insert a contaminated diskette into a diskette drive, the
contaminants can be transferred to the read/write head and from
the read/write head to the next diskette to be inserted in the
drive. The read/write head may also be damaged.
You may be able to recover the information from a diskette that
has had a substance spilled on it if you are positive that you
can rinse or wipe the substance from the diskette without
scratching the recording surface or leaving a residue. If you
are not sure, do not try to use the diskette. If you know you
can rinse the substance away, use only clean, cool water. Again,
be careful not to scratch the recording surface or get
fingerprints on it. Any kind of cleanser can contaminate the
diskette, and warm water can warp the diskette. Solvents can
dissolve and ruin the recording surface.
Worn diskettes
--------------
When diskettes are used for data exchange as defined in this
manual, recording surface wear is not a frequent problem.
However, because the read/write head is in contact with the
recording surface when reading or writing, wear does occur on
the surface over a period of time. Eventually, this wear can
cause areas on the recording surface in which readable records
cannot be written. (Of course, the handling, contamination, and
environmental concerns discussed earlier in this manual also
affect the length of time a diskette can remain in service.)
Some systems use diskettes to store the active processing file
for the system. When the diskette is used in this way, the
read/write head is repeatedly lowered to the diskette surface.
The repeated loading of the read/write head can increase the
wear rate. Ultimately, aside fom external factors, wear is
dependent upon the total usage of the individual tracks on the
diskette.
Suggestions for diskette operations
-----------------------------------
Your diskette operations will be smoother if you establish a
routine for tracking your diskettes, and learning approximately
how much service you can expect from each of them. The following
suggestions can help you set up and run your operation:
- Before using a new diskette, assign a serial number to
it, and record the number on the permanent diskette
label and in the space provided in the volume ID field.
(See Appendix C.)
- Keep a log of your diskettes by serial number and the
date you first used the diskette.
- Use your diskette log in combination with the
information on the diskette labels to track the average
length of time you receive satisfactory service from
your diskettes.
- Distribute your information over the diskette, so that
reading and writing occur over the entire recording
surface.
- Be prepared to handle unexpected problems. Some diskette
problems, especially those related to diskette damage,
are unpredictable, and can occur at any time.
- Make provision for an adequate recovery plan. Know what
you must do to ensure that your vital information is
safe. If necessary, make duplicate diskettes.
If a diskette causes error, you probably will have to replace
it. If your system allows you to reinitialize, try that, but if
the errors persist, discard the diskette. (See Appendix C.)
DISKETTE ADDRESSING AND LAYOUT
------------------------------
Diskettes contain libraries, or parts of libraries, in which
information is stored for safekeeping until needed. The concept
of a library also bears with it the idea that any information
stored there is accessible upon demand. Information
accessibility, then, requires a form of addressing that can be
used to find the information quickly. An address on a diskette
is composed of a track or cylinder number, a read/write head
number, and a record or sector number. Each of these numbers is
described in the following paragraphs.
The track
---------
Everything stored on the diskette is in the form of records
whose primary address is the track or cylinder number (the
cylinder concept is described later in this manual).
The diskette drive contains a carriage that can move the
read/write head to any of 77 distinct positions on the diskette
recording surface. A distinct movement of the read/write head is
required to get from one position to the next; therefore, if the
read/write head is held stationary in one position after
another, the path formed on the surface of the turning disk is
one of concentric circles, not a spiral. Each of the concentric
circles is a track. For addressing purposes, the tracks are
numbered from 00 through 76.
On a one-sided diskette, information is recorded on only one
side of the diskette; on a two-sided diskette, information is
recorded on both sides. The label side of a two-sided diskette
is side 1; the opposite side is side 0. A one-sided diskette
uses side 0 only. The diskette drive for two-sided diskettes has
a read/write head on each side of the diskette. Each track on
side 0 of a two-sided diskette has an associated track on side
1. The read/write heads are numbered to correspond to the
diskette side number.
The cylinder
------------
The name cylinder refers to both of the tracks available to the
read/write heads at any of the 77 locations on the two-sided
diskette. (Note that the terms track and cylinder are
interchangeable. Cylinder is also used to refer to the track
locations on a one-sided diskette.) The idea of the cylinder
comes from the imaginary, geometric figure formed by a line
drawn between the two read/write heads (through the diskette)
when the heads are stationary over their respective, moving
tracks. As the diskette moves between the heads, the line
between the heads forms a truncated cylinder. The cylinder
concept applies to any of the 77 tracks. Because the track and
cylinder locations are identical, cylinder addresses are also
numbered from 00 through 76.
The time saved justifies the use of the cylinder concept. It
takes time for the access mechanism to move the read/write heads
from track to track. However, by using an addressing scheme that
reads or writes first one side of the diskette and then the
other, two tracks can be utilized without moving the heads. The
diskette drive switches from head to head electronically.
Compared with any mechanical movement, electronic switching is
almost instantaneous.
The head
--------
The term head refers to the read/write head (or heads) in the
diskette drive. The read/write heads are described in detail
under "The diskette drive", earlier in this manual. The concept
of electronic head switching was mentioned in the preceding
paragraph.
The head number is either a hex 00 or a hex 01 to correspond to
the side of the diskette the read/write head is on. The head
number is always hex 00 on one-sided diskettes.
The sector
----------
To allow increasingly specific addressing, the track or cylinder
is uniformly divided into arcs called sectors. Each sector is
addressable.
Cylinder 0, side 0 always contains 26 sectors with 128 bytes per
sector. The number of sectors on cylinders 1 through 76 depends
on the diskette type and the number of bytes per sector for that
diskette type (see "IBM diskette types", later in this manual).
The address
-----------
In format, the address of any record on a diskette is a
composite of the elements of addressing just discussed: the
track or cylinder number, the read/write head number, and the
record or sector number. Each of these numbers is a two-digit
hexadecimal value. The digits are arranged in the address in
order of increasing definition. (In the following illustration,
X = a hexadecimal digit.)
+-------------> This is the number of the cylinder on which
| the record is to be written, or from which
| the record is to be read.
|
| +---------> This number specifies the read/write head
| | and, by doing that, also specifies which
| | side of the diskette is to be used.
| |
| | +-----> This is the number of the sector on which
| | | the record is to be written, or from which
| | | the record is to be read.
| XX XX XX |
+------------+--> This is the complete address.
The index cylinder
------------------
Cylinder 0 is the outermost cylinder on the diskette, and is
called the index cylinder. This cylinder is reserved for
information that describes the diskette and its contents. The
descriptive information includes volume and owner
identification, and other information associated with data set
(a group of related records) on the diskette. The information
about the data sets includes the name of the data set and the
address associated with the data set.
The continuous space occupied by or reserved for a particular
data set is called an extent. Extents also use addressing, to
achieve efficient reading and writing operations.
The address at the beginning of the extent is called the BOE
(beginning of extent). The address at the end of the extent is
called the EOE (end of extent). If a data set does not use all
of the space alloted to it by the BOE and EOE addresses, another
address for the end of the data is called the EOD (end of data).
The EOD address identifies the next unused area within the
extent, or shows that the data has been written to the EOE
address. The following illustration shows the relationships of
the BOE, EOD, and EOE.
This is the actual space currently
being used for the data set.
|
+------+-------+
BOE EOD EOE
| | |
V V V
-------------------------------------
+--------+----------+
|
This is the extent
(the area allotted for the data set).
Alternative cylinders
---------------------
The last two cylinders on the diskette, 75 and 76, are reserved
as alternative cylinders. That is, these cylinders are used as
replacements for cylinders that are defective. These two
cylinders are not used for storing information until they are
used as alternative cylinders.
IBM DISKETTE TYPES
------------------
IBM diskette 1
--------------
The IBM diskette 1, also known as a one-sided diskette, has a
recording surface on one side only. Because the diskette drive
can have a read/write head that contacts both sides, the side of
the diskette that is opposite the recording surface is also
finished to a smooth surface. The IBM diskette 1 is available in
three formats: 128, 256, and 512 bytes per sector.
128 bytes per sector
--------------------
(IBM Part 2305830)
This diskette has 77 tracks (00 through 76), with one track per
cylinder. Each cylinder on this diskette, including the index
cylinder (00), consists of 26 sectors with 128 bytes per sector.
Cylinders 1 through 74 are available for user data providing
1924 sectors or 246,272 bytes. Cylinders 75 and 76 are reserved
for alternative cylinder assignment.
When this diskette is used for basic data exchange, 73 cylinders
(1 through 73) are used. Cylinder 74 is not used. A basic data
exchange diskette provides 1898 sectors or 242,944 bytes.
256 bytes per sector
--------------------
(IBM Part 2305845)
This diskette has 77 tracks (00 through 76), with one track per
cylinder. The index cylinder (00) consists of 26 sectors with
128 bytes per sector. Cylinders 1 through 76 have 15 sectors per
cylinder. Each sector is 256 bytes long. Cylinders 1 through 74
are available for user data providing 1110 sectors or 284,160
bytes. Cylinders 75 and 76 are reserved for alternative cylinder
assignment.
512 bytes per sector
--------------------
(IBM Part 1669954)
This diskette has 77 tracks (00 through 76), with one track per
cylinder. The index cylinder (00) consists of 26 sectors with
128 bytes per sector. Cylinders 1 through 76 have 8 sectors per
cylinder. Each sector is 512 bytes long. Cylinders 1 through 74
are available for user data providing 592 sectors or 303,104
bytes. Cylinders 75 and 76 are reserved for alternative cylinder
assignment.
IBM diskette 2
--------------
The IBM diskette 2, also known as a two-sided diskette, has a
recording surface on each side. The IBM diskette 2 is available
in two formats: 128 and 256 bytes per sector.
128 bytes per sector
--------------------
(IBM Part 1766870)
This diskette has 77 cylinders (00 through 76). The index
cylinder (00) consists of 26 sectors with 128 bytes per sector
on each side of the diskette for a total of 52 sectors.
Cylinders 1 through 76 each have 26 sectors with 128 bytes per
sector on each side of the diskette for a total of 52 sectors
per cylinder. Cylinders 1 through 74 are available as primary
cylinders for data providing 3848 sectors or 492,544 bytes.
Cylinders 75 and 76 are reserved for alternative cylinder
assignment.
256 bytes per sector
--------------------
(IBM Part 2736700)
This diskette has 77 cylinders (00 through 76). The index
cylinder (00) consists of 26 sectors with 128 bytes per sector
on each side of the diskette for a total of 52 sectors.
Cylinders 1 through 76 each have 15 sectors with 256 bytes per
sector on each side of the diskette for a total of 30 sectors
per cylinder. Cylinders 1 through 74 are available as primary
cylinders for data providing 2220 sectors or 568,320 bytes.
Cylinders 75 and 76 are reserved for alternative cylinder
assignment.
IBM diskette 2D
---------------
The IBM diskette 2D is a two-sided, double-density diskette.
Two-sided, of course, means that the diskette has a recording
surface on each side. Double density means that the bits on this
diskette are written at twice the density of the bits on the IBM
diskettes 1 and 2.
256 bytes per sector
--------------------
(IBM Part 1766872)
This diskette has 77 cylinders (00 through 76). The index
cylinder (00) consists of 26 sectors with 128 bytes per sector
on side 0 and 26 sectors with 256 bytes per sector on side 1,
for a total of 52 sectors. Each 256-byte sector on cylinder 0
contains two 128-byte data set labels. Cylinders 1 through 76
each have 26 sectors with 256 bytes per sector on each side of
the diskette for a total of 52 sectors per cylinder. Cylinders 1
through 74 are available as primary cylinders for data providing
3848 sectors or 985,088 bytes. Cylinders 75 and 76 are reserved
for alternative cylinder assignment.
512 bytes per sector
--------------------
(IBM Part 1669044)
This diskette has 77 cylinders (00 through 76). The index
cylinder (00) consists of 26 sectors with 128 bytes per sector
on side 0 and 26 sectors with 256 bytes per sector on side 1,
for a total of 52 sectors. Each 256-byte sector on cylinder 0
contains two 128-byte data set labels. Cylinders 1 through 76
each have 15 sectors with 512 bytes per sector on each side of
the diskette for a total of 30 sectors per cylinder. Cylinders 1
through 74 are available as primary cylinders for data providing
2220 sectors or 1,136,640 bytes. Cylinders 75 and 76 are
reserved for alternative cylinder assignment.
1024 bytes per sector
---------------------
(IBM Part 1669045)
This diskette has 77 cylinders (00 through 76). The index
cylinder (00) consists of 26 sectors with 128 bytes per sector
on side 0 and 26 sectors with 256 bytes per sector on side 1,
for a total of 52 sectors. Each 256-byte sector on cylinder 0
contains two 128-byte data set labels. Cylinders 1 through 76
each have 8 sectors with 1024 bytes per sector on each side of
the diskette for a total of 16 sectors per cylinder. Cylinders 1
through 74 are available as primary cylinders for data providing
1184 sectors or 1,212,416 bytes. Cylinders 75 and 76 are
reserved for alternative cylinder assignment.
ACCESSORIES, DISKETTES, AND SUPPLIES
------------------------------------
IBM produces many supplies that are related directly to diskette
use. These supplies include items you can use for shipping,
storing, or working with diskettes. Your IBM IRD (Information
Records Division) representative can furnish these supplies to
you.
Sold in
Accessory multiples of Weight
-------------------------------- ------------ ----------------
Desk stand (20 diskettes) 1 2.9 kg (6.5 lbs)
Library case (10 diskettes) 5 2.5 kg (5.6 lbs)
Fiftyfile (50 diskettes) 1 0.7 kg (1.5 lbs)
Tab dividers for fiftyfile 5 -
Diskette magazine 5 3.7 kg (8.0 lbs)
10-pack slip case (10 diskettes) 30 7.7 kg (17 lbs)
Fan file 10 (10 diskettes) 1 1.5 kg (3.3 lbs)
Fan file 20 (20 diskettes) 1 2.2 kg (4.8 lbs)
Note: Diskettes are not included with these accessories. The
quantities of diskettes listed indicate the maximum number of
diskettes each accessory can contain.
Besides the accessories, IBM provides convenience kits
(including the diskettes) for certain systems and devices. The
convenience kits and the following diskettes and supplies are
available through your IRD (Information Records Division)
representative.
Sold in
Item multiples of Weight
--------------------------------- ------------ ------
Diskettes (Note 1) 10 1.4 kg (3.0 lbs)
Temporary adhesive identification 30 labels -
labels (rainbow pack (Note 2) (one pack)
or one color pack)
Protective envelopes (replacement) 50 1.1 kg (2.5 lbs)
Shipping carton for thirty
10-packs (Note 3) 25 24.9 kg (55 lbs)
Top and bottom pads for above carton 50 10.0 kg (22 lbs)
Shipping carton for twenty
10-packs (Note 3) 25 20.9 kg (46 lbs)
Top and bottom pads for above carton 50 7.3 kg (16 lbs)
Shipping carton for ten
10-packs (Note 3) 25 9.1 kg (20 lbs)
Top and bottom pads for above carton 50 4.1 kg (9 lbs)
Shipping carton for five
10-packs (Note 3) 25 6.4 kg (14 lbs)
Top and bottom pads for above carton 50 1.8 kg (4 lbs)
Shipping carton for one
10-pack (Note 3) 25 4.5 kg (10 lbs)
Shipping carton for one diskette 25 3.2 kg (7 lbs)
Die-cut spacer for a 10-pack (Note 3) 25 2.5 kg (5.5 lbs)
Zip-top plastic bags 10 -
Notes:
1: Diskettes are shipped in boxes of 10; each diskette is
enclosed in a protective envelope. Each box also contains a pack
of temporary adhesive labels.
2: A rainbow pack contains 30 labels, six each of red, blue,
yellow, green and gray.
3: 10-pack is a shortened title for the 10-pack slip case
included in the accessory list.
APPENDIX A. DISKETTE USERS
--------------------------
The following list of diskette using systems and devices is
divided by diskette types. Some of the systems and devices
appear in more than one place in the list because they use more
than one type of diskette. The list is current as of this
edition date and will be updated. Note, however, that new using
systems and devices may become available between editions or
revisions to this manual.
IBM diskette 1
--------------
128 bytes per sector
IBM 3540 diskette input/output unit
IBM 3601 finance communication controller, models 1, 2A, 2B, 3A, and 3B
IBM 3602 finance communication controller
IBM 3741 data station
IBM 3742 dual data station
IBM 3747 data converter
IBM 3773 communication terminal
IBM 3774 communication terminal
IBM 3775 communication terminal
IBM 3776 communication terminal
IBM 3777 communication terminal
IBM 3791 controller
IBM 3881 optical mark reader, model 3
IBM 3890 document processor
IBM 4331 processor
IBM 4962 disk storage unit, models 2, 2F, and 4
IBM 4964 diskette unit
IBM 4966 diskette magazine unit
IBM 5114 diskette unit
IBM 5231 controller, model 2
IBM 5265 point of sale terminal, all models
IBM 5320 system unit -- System/32
IBM 5340 system unit -- System/34, all models
IBM 5381 system unit -- System/38
IBM 7840 film thickness analyzer
IBM 7841 textile color analyzer
IBM 7842 coating analyzer
IBM 8101 storage and input/output unit
IBM 8130 processor
IBM 8140 processor
256 bytes per sector
IBM 3601 finance communication controller, models 1, 2A, 3A, and 3B
IBM 3602 finance communication controller
IBM 3631 plant communication controller, models 1A and 1B
IBM 3632 plant communication controller, models 1A and 1B
IBM 3791 controller
IBM 4962 disk storage unit, models 2, 2F, and 4
IBM 4964 diskette unit
IBM 4966 diskette magazine unit
IBM 5114 diskette unit
IBM 5381 system unit -- System/38
IBM 8101 storage and input/output unit
IBM 8130 processor
IBM 8140 processor
512 bytes per sector
IBM 4962 disk storage unit, models 2, 2F, and 4
IBM 4964 diskette unit
IBM 4966 diskette magazine unit
IBM 5114 diskette unit
IBM 5320 system unit -- System/32
IBM 5340 system unit -- System/34, all models
IBM 5381 system unit -- System/38
IBM 7840 film thickness analyzer
IBM 7841 textile color analyzer
IBM 7842 coating analyzer
IBM diskette 2
--------------
128 bytes per sector
IBM 4962 disk storage unit, models 2, 2F, and 4
IBM 4964 diskette unit
IBM 4966 diskette magazine unit
IBM 5114 diskette unit
IBM 5381 system unit -- System/38
256 bytes per sector
IBM 3601 finance communication controller, models 2B and 3B
IBM 3602 finance communication controller, models 1A and 1B
IBM 3631 plant communication controller, model 1B
IBM 3632 plant communication controller, models 1A and 1B
IBM 4962 disk storage unit, models 2, 2F, and 4
IBM 4964 diskette unit
IBM 4966 diskette magazine unit
IBM 5114 diskette unit
IBM 5381 system unit -- System/38
IBM diskette 2D
---------------
256 bytes per sector
IBM 4966 diskette magazine unit
IBM 5114 diskette unit
IBM 5265 point of sale terminal, models X3X and X4X
IBM 5340 system unit -- System/34, models X2X and X3X
IBM 5381 system unit -- System/38
IBM 8101 storage and input/output unit
IBM 8130 processor
IBM 8140 processor
512 bytes per sector
IBM 4966 diskette magazine unit
IBM 5114 diskette unit
IBM 5381 system unit -- System/38
1024 bytes per sector
IBM 4966 diskette magazine unit
IBM 5114 diskette unit
IBM 5340 system unit -- System/34, models X2X and X3X
IBM 5381 system unit -- System/38
APPENDIX B. DATA ORGANIZATION
-----------------------------
Physical and logical records
----------------------------
A record is a collection of related items of data that are
treated as a unit. You may be able to improve the efficiency of
your diskette operations by varying the way you organize the
records on your diskettes. The two choices discussed in this
appendix and shown in the examples are physical records and
logical records.
The sector defines the maximum length of a physical record. The
lengths are fixed for each type of diskette. These lengths are:
128, 256, 512, and 1024 bytes (see "IBM diskette types", earlier
in this manual). If, however, you choose not to restrict your
information to the fixed lengths of the physical records, you
may organize your information into logical records.
A logical record is independent of its physical environment
because it is not defined in physical terms, but rather in terms
of the information it contains. Therefore, the relationship
between logical and physical records varies. One example of data
organization may have logical records divided into portions that
occupy one or more physical records. Another example may have
several logical records occupying one physical record.
Blocking and spanning
---------------------
A block is a set of adjacent logical records that is recorded as
a unit. For basic data exchange and type H exchange, you can set
a block to any value greater than zero, but not greater than the
physical record length. For other types of diskette data
organization, the relationship of the block size to the physical
record size can be governed by the constraints of the system.
The following paragraph uses illustrations to help clarify the
explanations of blocking and spanning. In each of these
illustrations, the terms record and physical record appear. The
records shown on the top lines of the illustrations are logical
records.
You can place records on the diskette as blocked or unblocked,
spanned or unspanned, or in combinations of these four options,
for example:
Blocked: One record plus one or more records (or a segment of a
record) occupy a single block. The following examples are
illustrations of three possible combinations that form blocked
records:
+- Record -+--- Record ---+--- Record ---+-- Record --+ +- Record -+----
| Seg Segment| Segment Seg| | Seg
+----+ +------+--------------+ +----
==== Block ===== ==== Block ===== ==== Block ===== ==== Block =====
--- Phys Rec --- --- Phys Rec --- --- Phys Rec --- --- Phys Rec ---
+- Rec -+- Rec -+ +- Rec -+- Rec -+ +- Rec -+- Rec -+ +- Rec -+- Rec -+
==== Block ===== ==== Block ===== ==== Block ===== ==== Block =====
--- Phys Rec --- --- Phys Rec --- --- Phys Rec --- --- Phys Rec ---
+- Record -+- Record -+- Record -+ +- Record -+- Record -+- Record -+
============= Block ============= ============= Block =============
--- Phys Rec --- --- Phys Rec --- --- Phys Rec --- --- Phys Rec ---
Unblocked: One record exclusively occupies one or more blocks.
The following examples are illustrations of three possible
combinations that form unblocked records:
+--- Record ---+ +--- Record ---+ +--- Record ---+ +--- Record ---+
==== Block ===== ==== Block ===== ==== Block ===== ==== Block =====
--- Phys Rec --- --- Phys Rec --- --- Phys Rec --- --- Phys Rec ---
+- Record -+ +- Record -+ +- Record -+ +- Record -+
==== Block ===== ==== Block ===== ==== Block ===== ==== Block =====
--- Phys Rec --- --- Phys Rec --- --- Phys Rec --- --- Phys Rec ---
+------------- Record ------------+ +------------- Record ------------+
==== Block ===== ==== Block ===== ==== Block ===== ==== Block =====
--- Phys Rec --- --- Phys Rec --- --- Phys Rec --- --- Phys Rec ---
Spanned: One record extends beyond one block. The following
examples are illustrations of two possible combinations that
form spanned records:
+------------- Record ------------+ +------------- Record ------------+
==== Block ===== ==== Block ===== ==== Block ===== ==== Block =====
--- Phys Rec --- --- Phys Rec --- --- Phys Rec --- --- Phys Rec ---
+- Record -+--- Record ---+--- Record ---+-- Record --+ +- Record -+----
| Seg Segment| Segment Seg| | Seg
+----+ +------+--------------+ +----
==== Block ===== ==== Block ===== ==== Block ===== ==== Block =====
--- Phys Rec --- --- Phys Rec --- --- Phys Rec --- --- Phys Rec ---
Unspanned: One or more records do not extend beyond one block.
The following examples are illustrations of three possible
combinations that form unspanned records:
+--- Record ---+ +--- Record ---+ +--- Record ---+ +--- Record ---+
==== Block ===== ==== Block ===== ==== Block ===== ==== Block =====
--- Phys Rec --- --- Phys Rec --- --- Phys Rec --- --- Phys Rec ---
+- Record -+ +- Record -+ +- Record -+ +- Record -+
==== Block ===== ==== Block ===== ==== Block ===== ==== Block =====
--- Phys Rec --- --- Phys Rec --- --- Phys Rec --- --- Phys Rec ---
+- Rec -+- Rec -+ +- Rec -+- Rec -+ +- Rec -+- Rec -+ +- Rec -+- Rec -+
==== Block ===== ==== Block ===== ==== Block ===== ==== Block =====
--- Phys Rec --- --- Phys Rec --- --- Phys Rec --- --- Phys Rec ---
Blocked and Spanned: The following example illustrates the
combining of blocked and spanned records:
+- Record -+--- Record ---+--- Record ---+-- Record --+ +- Record -+----
| Seg Segment| Segment Seg| | Seg
+----+ +------+--------------+ +----
==== Block ===== ==== Block ===== ==== Block ===== ==== Block =====
--- Phys Rec --- --- Phys Rec --- --- Phys Rec --- --- Phys Rec ---
Blocked and Unspanned: The following examples illustrate the
combining of blocked and unspanned records:
+- Rec -+- Rec -+ +- Rec -+- Rec -+ +- Rec -+- Rec -+ +- Rec -+- Rec -+
==== Block ===== ==== Block ===== ==== Block ===== ==== Block =====
--- Phys Rec --- --- Phys Rec --- --- Phys Rec --- --- Phys Rec ---
+- Record -+- Record -+- Record -+ +- Record -+- Record -+- Record -+
============= Block ============= ============= Block =============
--- Phys Rec --- --- Phys Rec --- --- Phys Rec --- --- Phys Rec ---
Unblocked and Spanned: The following example illustrates the
combining of unblocked and spanned records:
+------------- Record ------------+ +------------- Record ------------+
==== Block ===== ==== Block ===== ==== Block ===== ==== Block =====
--- Phys Rec --- --- Phys Rec --- --- Phys Rec --- --- Phys Rec ---
Unblocked and Unspanned: The following examples illustrate the
combination of unblocked and unspanned records:
+--- Record ---+ +--- Record ---+ +--- Record ---+ +--- Record ---+
==== Block ===== ==== Block ===== ==== Block ===== ==== Block =====
--- Phys Rec --- --- Phys Rec --- --- Phys Rec --- --- Phys Rec ---
+- Record -+ +- Record -+ +- Record -+ +- Record -+
==== Block ===== ==== Block ===== ==== Block ===== ==== Block =====
--- Phys Rec --- --- Phys Rec --- --- Phys Rec --- --- Phys Rec ---
+--------- Record ---------+ +--------- Record ---------+
============= Block ============= ============= Block =============
--- Phys Rec --- --- Phys Rec --- --- Phys Rec --- --- Phys Rec ---
Sequential data
---------------
Sequential data organization provides a way in which you can
organize each of the diskette types. In the descriptions that
follow, the expression logical sequence means that the sectors
are read or written in sequence numerically; that is 1, 2, 3, 4,
and so on. For ease of illustration, these examples show reading
or writing beginning at track or cylinder 1; however, in
practice, reading or writing can begin at any track or cylinder.
Because the organization for the IBM diskette 2 is identical to
that for the IBM diskette 2D, only one description is given.
The IBM diskette 1: A one-sided diskette that requires only one
read/write head. Reading or writing sequentially on this
diskette proceeds as follows:
1. Start at track (cylinder) 1; in logical sequence, read
or write each sector of the track.
2. Move to track (cylinder) 2; in logical sequence, read or
write each sector of the track.
3. Move to track (cylinder) 3; in logical sequence, read or
write each sector of the track.
4. Continue in this manner to the EOD.
The IBM diskettes 2 and 2D: Two-sided diskettes that require
read/write heads on each side. The diskette drive switches from
read/write head 0 to read/write head 1 electronically. Reading
or writing sequentially on this diskette proceeds as follows:
1. Start at cylinder 1 with read/write head 0; in logical
sequence, read or write each sector of the track.
2. Still on cylinder 1, switch to head 1; in logical
sequence, read or write each sector of the track.
3. Move to cylinder 2, switch back to head 0; in logical
sequence, read or write each sector of the track.
4. Still on cylinder 2, switch to head 1; in logical
sequence, read or write each sector of the track.
5. Move to cylinder 3, switch back to head 0; in logical
sequence, read or write each sector of the track.
6. Still on cylinder 3, switch to head 1; in logical
sequence, read or write each sector of the track.
7. Continue in this manner, switching from one side of the
diskette to the other... to the EOD.
APPENDIX C. INITIALIZATION AND TRACK FORMAT
-------------------------------------------
Initialization
--------------
Initialization is a part of the process of preparing a diskette
for shipment to the purchaser. Each new diskette is initialized
following a careful inspection, to ensure that it contains no
manufacturing defects that could prevent accurate writing and
reading. Initialization writes the label information and data
addresses on the diskette recording surface. The formats used
for the index cylinder and the data set labels are discussed in
Appendix D and Appendix E.
Reinitialization
Some IBM systems have facilities to reinitialize diskettes. This
process permits you to change the size of the sectors on a
diskette, or to bypass a maximum of two defective cylinders or
tracks. Note that, unless your system has a special provision
for saving the information contained on the diskette, all the
information is lost during reinitialization.
In this process, the system flags a defective cylinder by
filling all of the ID fields on that cylinder with binary ones.
The system then writes the cylinder number from the defective
cylinder into the ID field of the next physical cylinder. This
means that the ID from every cylinder whose physical cylinder
number is higher in value than the defective cylinder is moved
up to the next respective cylinder.
The physical cylinder numbers of defective cylinders are
recorded in the error map sector (sector 05 of side 0 of the
index cylinder). When the device encounters a defective cylinder
during read or write operations, the read/write head
automatically moves to the next physical cylinder.
Track format
------------
Except for the index cylinder, each track on a new diskette is
initialized to the same basic format. The information in some of
the sectors varies with the diskette type. For more details on
the contents of the index cylinder and cylinders 1 through 76,
see Appendix D and Appendix E.
The following illustration shows how the tracks are formatted at
initialization. Also shown on the illustration are numbers that
serve as keys to the notes that describe the particular fields.
: : : :
+-+--------+ +----------+
/ | Last | | Last |
/ | sector | | sector |
/+---+--------+------+----------+
// | Gap | | Preindex |
// | | | Gap |
O--Index+========+ +==========+ ID field of Sector 01
\\ | Sector | | Sync | |
\\ | 01 | | field | | (Note 1 below)
\+-+--------+ +----------+ |
\ | Sector |\ | AM1 | | Hex FE (identifies ID field)
\| 02 | \ +----------+ |
+--------+ + | Cylinder | | (see details below)
| Sector | | | number | |
| 03 | | +----------+ |
+--------+ | | Head | | (see below)
: : | | number | |
| +----------+ |
| | Record | | (see below)
| | number | |
| +----------+ |
| | Physical | | (see below)
| | record | |
| | length | |
| +----------+ |
| | CRC | | (Note 2)
| +----------+-+
| | Post-ID |
| | Gap |
| +----------+-+--> Data field of Sector 01
| | Sync | |
| | field | |
| +----------+ |
| | AM2 | | (Note 3)
| +----------+ |
| | Number of| |
| | bytes | | (Note 4)
| +----------+ |
+ | CRC | |
\ +----------+-+
\ | Postdata |
\| gap |
+----------+-+--> ID field of Sector 02
| Sync | |
| field | |
+----------+ |
| AM1 | |
+----------+ |
| ID field | | (Note 5)
: : :
where
Cylinder number:
hex 00 through hex 4A (decimal 0 through 74; cylinders 75 and 76
are used as alternative cylinders).
Head number:
hex 00 for one-sided diskettes and side 0 for two-sided
diskettes;
hex 01 for side 1 of two-sided diskettes.
Record number:
Hex 01 through hex 1A for 128-bytes-per-sector format diskette 1
Hex 01 through hex 1A for 128-bytes-per-sector format diskette 2
Hex 01 through hex 1A for 256-bytes-per-sector format diskette 2D
Hex 01 through hex 0F for 256-bytes-per-sector format diskette 1
Hex 01 through hex 0F for 256-bytes-per-sector format diskette 2
Hex 01 through hex 0F for 512-bytes-per-sector format diskette 2D
Hex 01 through hex 08 for 512-bytes-per-sector format diskette 1
Hex 01 through hex 08 for 1,024-bytes-per-sector format diskette 2D
Physical record length:
Hex 00 for 128-bytes-per-sector format
Hex 01 for 256-bytes-per-sector format
Hex 02 for 512-bytes-per-sector format
Hex 03 for 1,024-bytes-per-sector format
Note 1:
Binary zero sync bytes
Note 2:
Cyclic redundancy check. The check bytes are generated during a
write operation, and are used during both write and read
operations to verify that the data is correct.
Note 3:
Various systems have the ability to modify records or the
locations of records. These modifications are as follows:
- Logically delete a record
- Move a record from a defective sector to the next
sequential sector
- Move a record from a defective sector to an alternative
sector
These modifications are made by changing the contents of the
address marker AM2 and the first character of the data field
that immediately follows AM2. When the first character of the
data field changes, the data field changes to a control field
that designates what type of modification was made.
Note: The address marker AM2 usually contains a hex FB. When any
of the three modifications is necessary, AM2 is changed to hex
F8. F8 alerts the device to check the first character of the
next field.
Note 4:
128; 256; 512; or 1,024 bytes.
The value of the first character of this field specifies the
type of modification that has affected the record that
previously occupied the sector. The characters used and their
significance are:
- D, which means delete the record. During subsequent read
operations, the device ignores the remaining contents of
this sector.
- F, which means move the record to the next sequential
sector. During subsequent read operations, the device
ignores the remaining contents of this sector, and
searches for the record in the next sequential sector.
- . (period), which means move the record to a sector that
has been allocated as an alternative sector. The address
of the alternative sector is written in the error
directory (sector 05 on side 0 of the index cylinder).
During subsequent read operations, the device reads the
period, and searches for the sector address in the error
directory (error map).
Note 5:
The ID field contains the sync field, address marker 1, the
address and length of the record, and CRC bits. From this
information, the system can identify and locate the record. If
the cylinder is defective, all the ID fields on that cylinder
are filled with binary ones.
APPENDIX D. INDEX CYLINDER LAYOUT
---------------------------------
Every new IBM diskette is inspected and initiated. The following
table lists the sectors of the index cylinder, the byte
positions within the sectors, the purposes for those positions,
and the values written in the byte positions. Occasionally, you
will find a number in parentheses in the Initialized to: line.
These numbers represent the various diskette types:
(128-1) = a one-sided diskette with 128-bytes per sector
(256-1) = a one-sided diskette with 256-bytes per sector
(512-1) = a one-sided diskette with 512-bytes per sector
(128-2) = a two-sided diskette with 128-bytes per sector
(256-2) = a two-sided diskette with 256-bytes per sector
(256-2D) = a two-sided, double-density diskette with 256-bytes per sector
(512-2D) = a two-sided, double-density diskette with 512-bytes per sector
(1024-2D) = a two-sided, double-density diskette with 1024-bytes per sector
Where there is a difference in the value written for a
particular diskette type, the Initialized to: line shows both
the number that represents the diskette type and the value
assigned to that diskette type. The following example from the
Initialized to: line shows that the value for two of the
diskette types differs from the value assigned to the other
diskette types. The values are shown in hexadecimal:
(128-1) = Hex 40
(256-1) = Hex C2
(512-1) = Hex 40
(128-2) = Hex 40
(256-2) = Hex C2
(256-2D) = Hex 40
(512-2D) = Hex 40
(1024-2D) = Hex 40
The index cylinder on a new IBM diskette
Format: Side
Sector
Positions and use
Initialized to:
Side: 0
Sector: 01
Positions and use: Positions 1-80 are reserved for IPL and IMPL.
Initialized to: Hex 40
Side: 0
Sector: 01
Positions and use: Positions 81-128 are reserved for IPL and IMPL.
Initialized to: Hex 00
0
02
Positions 1-80 are reserved for IPL and IMPL.
Hex 40
0
02
Positions 81-128 are reserved for IPL and IMPL.
Hex 00
0
03
Positions 1-80 are reserved for system scratch.
Hex 40
0
03
Positions 81-128 are reserved for system scratch.
Hex 00
0
04
Positions 1-80 are reserved.
Hex 40
0
04
Positions 81-128 are reserved.
Hex 00
0
05
Positions 1-5 = ERMAP. (ERMAP is a label that identifies this
record as an error map.)
ERMAP
0
05
Position 6 is a separator, and contains a blank.
Hex 40
0
05
Positions 7-8 contain blanks if no defective cylinders exist. If
defective cylinders exist, positions 7-8 contain the number of
the first defective physical cylinder.
Hex 40
0
05
Position 9 is a blank if no defective cylinder exists. If one or
more defective cylinders exist, position 9 contains a zero.
Hex 40
0
05
Position 10 is a separator, and contains a blank.
Hex 40
0
05
Positions 11-12 contain blanks if one or no defective cylinder
exists. If more than one defective cylinder exists, positions
11-12 contain the number of the second defective physical
cylinder.
Hex 40
0
05
Position 13 is a blank if one or no defective cylinder exists.
If more than one defective cylinder exists, position 13 contains
a zero.
Hex 40
0
05
Position 14 is a separator, and contains a blank.
Hex 40
0
05
Positions 15-22 are reserved.
Hex 40
0
05
Position 23 is the defective record indicator. It contains a
blank to indicate that no defective records to be handled by the
alternative physical record method are contained within the data
portion of any data set extent on the volume. At least one such
defective record exists if position 23 contains a D.
Hex 40
0
05
Position 24 is the error directory indicator. It contains a
blank to indicate that no format or alternative physical record
relocation has been previously specified. B or C indicates the
defective physical records have had their contents relocated to
a data set named ERRORSET. B indicates the addresses of the
defective physical records have been recorded in the error
directory in the discontinuous binary format (OCHR). C indicates
that the addresses of the defective physical records have been
recorded in the error directory in the character decimal format
(bCCHRR).
(128-1) = Hex 40
(256-1) = Hex C2
(512-1) = Hex 40
(128-2) = Hex 40
(256-2) = Hex C2
(256-2D) = Hex 40
(512-2D) = Hex 40
(1024-2D) = Hex 40
0
05
Positions 25-72 are the error directory. This directory contains
entries of addresses of physical records containing one or more
defects. In the discontinuous binary format (0CHR), this field
can contain addresses of up to 12 relocated physical records. In
the character decimal format (bCCHRR), this field can contain
the address of up to 8 relocated physical records. The relocated
records are contained in a data set named ERRORSET in the same
sequence as the addresses in the directory. Unused positions of
the error directory must contain binary zeros if position 24
contains a B. If position 24 contains a C, unused portions of
the error directory must contain blanks.
(128-1) = Hex 40
(256-1) = Hex 00
(512-1) = Hex 40
(128-2) = Hex 40
(256-2) = Hex 00
(256-2D) = Hex 40
(512-2D) = Hex 40
(1024-2D) = Hex 40
0
05
Positions 73-80 are reserved.
Hex 40
0
05
Positions 81-128 are padded.
(128-1) = Hex 00
(256-1) = Hex 00
(512-1) = Hex 00
(128-2) = Hex 00
(256-2) = Hex 00
(256-2D) = Hex 40
(512-2D) = Hex 40
(1024-2D) = Hex 40
0
06
Positions 1-80 are reserved.
Hex 40
0
06
Positions 81-128 are reserved.
Hex 00
0
07
This sector is called the volume label. Various fields in this
sector identify the diskette: the owner, security, sequence, and
length of physical records.
Positions 1-4 identify the sector as a volume label.
VOL1
0
07
Positions 5-10 are called the volume identifier. This field can
contain the same volume identifier (serial number) that is
written on the diskette permanent label. The ID consists of one
to six digits or letters. The first character must be in
position 5 of the sector, and any unused positions in the field
to the right of the ID data must be blanks. No blanks are
allowed between digits or letters in this field. When the
diskette is initialized by an IBM device, this field will
contain the value specified as part of the initialization
procedure.
IBMIRD
0
07
Position 11 is the volume accessibility field. A blank in this
field permits access to the diskette. Any nonblank character in
this field means additional qualifications are required for
further access.
Hex 40
0
07
Positions 12-37 are reserved.
Hex 40
0
07
Positions 38-51 are called the owner identifier field. This
field is not used by some systems.
Hex 40
0
07
Positions 52-64 are reserved.
Hex 40
0
07
Position 65 is the label extension indicator. The character in
this position (space or 1 through 9) indicates the number of
cylinders (in addition to cylinder 0) that are allocated as
system area needed for data set labels. A non-space value is
only allowed on the IBM diskette 2D. The indicator values mean:
Space = No additional cylinders allocated
(all data set labels are on cylinder 0).
1 = Cylinder 1 is reserved as system area.
2 = Cylinders 1 and 2 are reserved as system area.
3 = Cylinders 1, 2, and 3 are reserved as system area.
4-9 = A maximum of nine additional cylinders can be reserved
as system area.
The value in position 65 must be entered when the diskette is
initialized and must not be changed during normal label
processing. Using systems are not required to read or write the
data sets whose labels are in the extended system area, but all
systems must be able to detect position 65.
When the system does not support label extension, allocation
must be prohibited if position 65 equals any value other than
space. Data sets with labels on cylinder 0 can be read or
updated, as long as the data set extents are not modified.
However, any data sets that have labels in the extended system
area are not accessible, and must not be identified as type H
exchange.
Hex 40
0
07
Positions 66-71 are reserved.
Hex 40
0
07
Position 72 is the volume surface indicator, and contains either
a blank, a 2, or an M. A blank indicates one recording surface;
2 indicates two recording surfaces; M indicates two double-
density recording surfaces.
(128-1) = Hex 40
(256-1) = Hex 40
(512-1) = Hex 40
(128-2) = Hex F2
(256-2) = Hex F2
(256-2D) = Hex D4
(512-2D) = Hex D4
(1024-2D) = Hex D4
0
07
Position 73 is the extent arrangement indicator, and contains a
blank or a P. A blank indicates there are no special constraints
on the arrangement of extents, data set labels, or unallocated
space on this diskette. P indicates the extents must be adjacent
and must begin at cylinder 1, head 0, sector 1. P also indicates
that the data set labels must begin at cylinder 0, head 0,
sector 8, and must be in the same sequence as the extents they
describe. P also indicates that all unallocated space must
follow the last data set extent on the volume. If any unused
space is created elsewhere, the extents must be rearranged to
eliminate the space, or this field must be changed to a blank.
Hex 40
0
07
Position 74 is the special requirements indicator, and contains
a blank or an R. A blank indicates that there are no special
requirements for accessing data on this volume. R indicates that
some of the data sets were recorded in a logically non-
sequential manner.
Hex 40
0
07
Position 75 is reserved.
Hex 40
0
07
Position 76 identifies the length of the physical record
(sector) on cylinders 1 through 76, and contains a blank, 1, 2,
or 3:
Blank = 128 bytes
1 = 256 bytes
2 = 512 bytes
3 = 1024 bytes
(128-1) = Hex 40
(256-1) = Hex F1
(512-1) = Hex F2
(128-2) = Hex 40
(256-2) = Hex F1
(256-2D) = Hex F1
(512-2D) = Hex F2
(1024-2D) = Hex F3
0
07
Positions 77-78 are the physical record (sector) sequence code.
This field contains blanks or the characters 01 through 13, and
indicates the physical sequence of sectors. A blank or 1
indicates the sectors are physically sequential. Otherwise, this
field is used a an increment to determine the next physical
sector. Diskettes initialized on an IBM device may have a value
specified as part of the initialization procedure.
Hex 40
0
07
Position 79 is reserved.
Hex 40
0
07
Position 80 is the label standard version field. W indicates
that IBM standard labels are on the diskette.
W
0
07
Positions 81-128 are padded.
(128-1) = Hex 00
(256-1) = Hex 00
(512-1) = Hex 00
(128-2) = Hex 00
(256-2) = Hex 00
(256-2D) = Hex 40
(512-2D) = Hex 40
(1024-2D) = Hex 40
Side: 0, Sectors: 08-26 and Side: 1, Sectors: 01-26
These sectors are used to record the data set labels that define
the data sets recorded on cylinders 01 through 74 of the
diskette. Sectors 09 through 26 on side 0 and sectors 01 through
26 on side 1 are initialized as deleted records. (See Appendix
E.)
APPENDIX E. DATA SET LABEL LAYOUT
---------------------------------
Every new IBM diskette is inspected and initialized. The
following table lists the character positions and labels,
descriptions of the labels, and the values written in the
character positions. Occasionally, you will find a number in
parentheses in one or both of the Initialized to: line. These
numbers represent the various diskette types:
(128-1) = a one-sided diskette with 128-bytes per sector
(256-1) = a one-sided diskette with 256-bytes per sector
(512-1) = a one-sided diskette with 512-bytes per sector
(128-2) = a two-sided diskette with 128-bytes per sector
(256-2) = a two-sided diskette with 256-bytes per sector
(256-2D) = a two-sided, double-density diskette with 256-bytes per sector
(512-2D) = a two-sided, double-density diskette with 512-bytes per sector
(1024-2D) = a two-sided, double-density diskette with 1024-bytes per sector
Where there is a difference in the value written for a
particular diskette type, the Initialized to: lines show both
the number that represents the diskette type and the value
assigned to that diskette type. The following example from the
Initialized to: lines shows that the value for three of the
diskette types differs from the value assigned to the other
diskette types. The values are shown in hexadecimal (the
character b represents a blank):
(128-1) = DDR1
(256-1) = Dbbb
(512-1) = Dbbb
(128-2) = DDR1
(256-2) = Dbbb
(256-2D) = DDR1
(512-2D) = DDR1
(1024-2D) = DDR1
Data set labels on a new IBM diskette
Format: Character position
Label
Description
Initialized to: Sector 08, Side 0
Sectors 09-26, Side 0 and Sectors 01-26, Side 1
Character position: 1-4
Label: Label ID (identifier)
Description: Label identifier for system application
Initialized to:
Sector 08, Side 0: DDR1
Sectors 09-26, Side 0 and Sectors 01-26, Side 1:
(128-1) = DDR1
(256-1) = Dbbb
(512-1) = Dbbb
(128-2) = DDR1
(256-2) = Dbbb
(256-2D) = DDR1
(512-2D) = DDR1
(1024-2D) = DDR1
Character position: 5
Label: (none)
Description: Position 5 is reserved
Initialized to:
Sector 08, Side 0: b
Sectors 09-26, Side 0 and Sectors 01-26, Side 1: b
6-22
Data set identifier
User name for data set. The name must be 1 to 17 characters. The
first character must be alphabetic. No blanks are allowed
between characters. Duplicate names are not permitted on the
same diskette. For basic data exchange and type H exchange, only
the first 8 characters are used. The names ERRORSET, SYSAREA,
and ERMAP are reserved for special use.
DATAb...b
(128-1) = DATA09...b through DATA26b...b
(256-1) = b...b
(512-1) = b...b
(128-2) = DATA09b...b through DATA26b...b
(256-2) = b...b
(256-2D) = DATA09b...b through DATA26b...b
and DATA27b...b through DATA77b...b (**)
(512-2D) = DATA09b...b through DATA26b...b
and DATA27b...b through DATA77b...b (**)
(1024-2D) = DATA09b...b through DATA26b...b
and DATA27b...b through DATA77b...b (**)
Note **: These are the odd-numbered bytes (DATA27, 29, 31, ...,
75, 77); the even-numbered bytes are in positions 134 through
150.
23-37
Block length
This field contains a numeric value that specifies the maximum
number of characters per block. At label creation, the contents
must be entered. Blocks must begin on physical record
boundaries. For a basic exchange data set, this field must be 1-
128. For a type H data set, this field must be 1-256.
Sector 08, Side 1:
(128-1) = bb080
(256-1) = 00256
(512-1) = bb512
(128-2) = bb128
(256-2) = 00256
(256-2D) = bb256
(512-2D) = bb512
(1024-2D) = b1024
Sectors 09-26, Side 0 and Sectors 01-26, Side 1:
(128-1) = bb080
(256-1) = bbbbb
(512-1) = bb512
(128-2) = bb128
(256-2) = bbbbb
(256-2D) = bb256
(512-2D) = bb512
(1024-2D) = b1024
28
Record attribute
Indicates blocking used within the data set. When the exchange
type indicator (position 44) is a blank or H, this field must be
a blank.
b = Records unblocked, unspanned
R = Records blocked, spanned
B = Records blocked, unspanned
S = Records unblocked, spanned
b
b
29-33
Beginning of extent (BOE)
Identifies the address of the first sector of the data set.
Positions 29-30 contain the cylinder number, position 31
contains the head number, and positions 32-33 contain the sector
number. (Some systems use a logical record number. In this case,
position 74 of the volume label contains an R.)
Sector 08, Side 1: 01001
Sectors 09-26, Side 0 and Sectors 01-26, Side 1:
(128-1) = 74001
(256-1) = bbbbb
(512-1) = 75001
(128-2) = 75001
(256-2) = bbbbb
(256-2D) = 75001
(512-2D) = 75001
(1024-2D) = 75001
34
Physical record length
Indicates physical record length:
b = 128 bytes per record
1 = 256 bytes per record
2 = 512 bytes per record
3 = 1024 bytes per record
The value in this field must be the same as position 76 of the
volume label. When the exchange type indicator (position 44) is
a blank, this field must be a blank. When position 44 is H, this
field must contain a 1.
Sector 08, Side 1:
(128-1) = b
(256-1) = 1
(512-1) = 2
(128-2) = b
(256-2) = 1
(256-2D) = 1
(512-2D) = 2
(1024-2D) = 3
Sectors 09-26, Side 0 and Sectors 01-26, Side 1:
(128-1) = b
(256-1) = b
(512-1) = 2
(128-2) = b
(256-2) = b
(256-2D) = 1
(512-2D) = 2
(1024-2D) = 3
35-39
End of extent (EOE)
Identifies the address of the last sector reserved for this data
set, using the same format as BOE.
Sector 08, Side 0:
(128-1) = 73026
(256-1) = 74015
(512-1) = 74108
(128-2) = 74126
(256-2) = 74115
(256-2D) = 74126
(512-2D) = 74115
(1024-2D) = 74108
Sectors 09-26, Side 0 and Sectors 01-26, Side 1:
(128-1) = 73026
(256-1) = bbbbb
(512-1) = 74108
(128-2) = 74126
(256-2) = bbbbb
(256-2D) = 74126
(512-2D) = 74115
(1024-2D) = 74108
40
Record/block format
This field contains a blank or F, and indicates fixed-length
records in fixed blocks. When the exchange type indicator
(position 44) is a blank or H, this field must be blank.
b
b
41
Bypass indicator
Indicates a data set to be skipped during exchange or copy
operations when transmitting or transferring the data sets on
the volume. If this position is set to a blank, the data set is
transferred; if it is set to B, the data set is not transferred.
b
b
42
Data set security
A blank indicates the data set is not secured (can be accessed).
A non-blank character means restricted access. When the position
is non-blank, the volume accessibility indicator in the volume
label (track 00, sector 07) must also be non-blank.
b
b
43
Write protect
If this data set contains a P, the data set can be read only.
This field must be a blank to allow both reading and writing.
b
b
44
Exchange type indicator
A blank indicates the data set can be used for basic data
exchange; H indicates the data set is a type H data set. An E
indicates that additional label checking must be performed in
order to exchange the data set. (See Appendix F.)
Sector 08, Side 0:
(128-1) = b
(256-1) = E
(512-1) = E
(128-2) = b
(256-2) = E
(256-2D) = H
(512-2D) = E
(1024-2D) = E
Sectors 09-26, Side 0 and Sectors 01-26, Side 1:
(128-1) = b
(256-1) = b
(512-1) = E
(128-2) = b
(256-2) = b
(256-2D) = H
(512-2D) = E
(1024-2D) = E
45
Multivolume indicator
A blank in this field indicates a data set is wholly contained
on this diskette; C indicates a data set is continued on another
diskette; L indicates the last diskette on which a continued
data set resides.
b
b
46-47
Volume sequence number
Specifies the sequence of volumes in a multivolume data set. The
sequence must be consecutive, beginning with 01 (to a maximum of
99). Blanks indicate that volume sequence checking is not to be
performed on this volume and all subsequent volumes of a
multivolume data set.
bb
bb
48-53
Creation date
May be used to record the date the data set was created. The
format is YYMMDD, where YY is the low-order 2 digits of the
year, MM is a 2-digit representation of the month, and DD is a
2-digit representation of the day of the month. Blanks indicate
that the creation date is not significant.
bbbbbb
bbbbbb
54-57
Record length
At label creation, record length must be defined. A blank means
the record length equals the block length defined in position
23. (A blank or H in position 44 also means record length equals
block length; therefore, this field can be ignored.)
bbbb
bbbb
58-62
Offset to next record space
This field indicates the starting position for the next
sequential record relative to the end of the last block before
EOD (end of data) and contains blanks or a decimal value to be
used as a negative displacement. Blanks mean zero displacement
from the next block (starts at EOD address). This field is used
only in conjunction with blocked records.
bbbbb
bbbbb
63-66
(none)
Positions 63-66 are reserved.
bbbb
bbbb
67-72
Expiration date
May be used to contain the date the data set (and its label) may
be deleted. The format is the same as creation date (positions
48-53). All blanks indicate the data set is considered expired.
All 9s indicate the data set will never expire.
bbbbbb
bbbbbb
73
Verify/copy indicator
This field must contain a blank, V, or C. A blank must be
entered here when the data set is created. Systems that support
verification enter a V to indicate the data set has been
verified. Systems that support copy verification enter a C to
indicate the data has been successfully transferred to another
medium (for example, tape, transmission network). Do not enter C
for partial data set copy or for null data set.
b
b
74
Data set organization
This field must contain a blank, S, or D. A blank or S indicates
sequential data organization. (See Appendix B.) D means some
organization that does not permit the sequential relocation
method of processing defective physical records. When the
exchange type indicator (position 44) is a blank or H, this
field must contain a blank.
b
b
75-79
End of data (EOD)
Identifies the address of the next unused sector within the data
set extent, using the same format as BOE. If this field is the
same as BOE, the extent contains a null data set. If this field
contains the address of the next block beyond the extent (for
unblocked, unspanned records), the entire extent has been used.
For blocked or spanned records, this field must be used with
offset to next record space (positions 58-62) to determine the
end of actual data recorded.
Sector 08, Side 0: 01001
Sectors 09-26, Side 0 and Sectors 01-26, Side 1:
(128-1) = 74001
(256-1) = bbbbb
(512-1) = 75001
(128-2) = 75001
(256-2) = bbbbb
(256-2D) = 75001
(512-2D) = 75001
(1024-2D) = 75001
80
(none)
Position 80 is reserved.
b
b
81-128
Positions 81-128 are padded.
Sector 08, Side 0:
(128-1) = Hex 00
(256-1) = Hex 00
(512-1) = Hex 00
(128-2) = Hex 00
(256-2) = Hex 00
(256-2D) = Hex 40
(512-2D) = Hex 40
(1024-2D) = Hex 40
Sectors 09-26, Side 0 and Sectors 01-26, Side 1:
(128-1) = Hex 00
(256-1) = Hex 00
(512-1) = Hex 00
(128-2) = Hex 00
(256-2) = Hex 00
(256-2D) = Hex 40
(512-2D) = Hex 40
(1024-2D) = Hex 40
The following positions apply only to the double-density
diskettes (2D), Side 1:
129-132
(none)
Same as positions 1-4.
Sectors 01-26, Side 1:
(256-2D) = DDR1
(512-2D) = DDR1
(1024-2D) = DDR1
133
(none)
Same as position 5.
Sectors 01-26, Side 1: b
134-150
(none)
Same as positions 6-22.
Sectors 01-26, Side 1:
(256-2D) = DATA28b...b through DATA78b...b (**)
(512-2D) = DATA28b...b through DATA78b...b (**)
(1024-2D) = DATA28b...b through DATA78b...b (**)
Note **: These are the even-numbered bytes (DATA28, 30, 32, ...,
76, 78); the odd-numbered bytes are in positions 6 through 22.
151-155
(none)
Same as positions 23-27.
Sectors 01-26, Side 1:
(256-2D) = bb256
(512-2D) = bb512
(1024-2D) = b1024
156
(none)
Same as position 28.
b
157-161
(none)
Same as positions 29-33.
Sectors 01-26, Side 1:
(256-2D) = 75001
(512-2D) = 75001
(1024-2D) = 75001
162
(none)
Same as position 34.
Sectors 01-26, Side 1:
(256-2D) = 1
(512-2D) = 2
(1024-2D) = 3
163-167
(none)
Same as positions 35-39.
Sectors 01-26, Side 1:
(256-2D) = 74126
(512-2D) = 74115
(1024-2D) = 74108
168
(none)
Same as position 40.
b
169
(none)
Same as position 41.
b
170
(none)
Same as position 42.
b
171
(none)
Same as position 43.
b
172
(none)
Same as position 44.
Sectors 01-26, Side 1:
(256-2D) = H
(512-2D) = E
(1024-2D) = E
173
(none)
Same as position 45.
b
174-175
(none)
Same as positions 46-47.
bb
176-181
(none)
Same as positions 48-53.
bbbbbb
182-185
(none)
Same as positions 54-57.
bbbb
186-190
(none)
Same as positions 58-62.
bbbbb
191-194
(none)
Same as positions 63-66.
bbbb
195-200
(none)
Same as position 67-72.
bbbbbb
201
(none)
Same as position 73.
b
202
(none)
Same as position 74.
b
203-207
(none)
Same as positions 75-79.
Sectors 01-26, Side 1:
(256-2D) = 75001
(512-2D) = 75001
(1024-2D) = 75001
208
(none)
Same as position 80.
b
209-256
(none)
Same as positions 81-128.
Sectors 01-26, Side 1:
(256-2D) = Hex 40
(512-2D) = Hex 40
(1024-2D) = Hex 40
APPENDIX F. DATA EXCHANGE
-------------------------
Data exchange is the name given to a process whereby information
is written on a diskette at one system and used in another
system. To ensure that the exchange of information can be
accomplished efficiently and without errors, certain standard
formats have been established. These formats are basic data
exchange, type H data exchange, and type E general exchange.
Basic data exchange
-------------------
Basic exchange data sets have requirements assuring that
diskettes may be exchanged between systems capable of reading
and writing both the IBM diskette 1 and the IBM diskette 2.
For basic exchange data sets, the exchange type indicator (data
set label position 44) must be a blank. This means:
- The data set is organized sequentially.
- The records are a maximum of 128 bytes long.
- The records are of fixed length, unblocked, and unspanned.
- The physical record length is 128 bytes.
- The data set identifier (data set label positions 6
through 22) is not longer than eight positions.
Additional requirements vary between the IBM diskette 1 and 2.
IBM diskette 1 must:
- Be initialized with physically sequential records
(Volume label positions 77 and 78 are specified either
bb (blank) or 01.)
- Have basic exchange data sets on tracks 1 through 73 only.
IBM diskette 2 must:
- Be initialized with physically sequential records
(Volume label positions 77 and 78 may be specified bb
(blank) or 01 through 13.)
- Have basic exchange data sets on cylinders 1 through 74.
No diskette containing basic exchange data sets is allowed to
use alternative physical record relocation.
Type H data exchange
--------------------
Type H exchange data sets have requirements assuring that
diskettes may be exchanged between systems capable of reading
and writing the IBM diskette 2D.
For type H exchange data sets, the exchange type indicator (data
set label position 44) must be an H. This means:
- The data set is organized sequentially.
- The records are a maximum of 256 bytes long.
- The records are of fixed length, unblocked, and unspanned.
- The physical record length is 256 bytes.
- The data set identifier (data set label positions 6
through 22) is not longer than eight positions.
In addition, a diskette containing type H exchange data sets may
be initialized with physically non-sequential records (volume
label positions 77 and 78 are space or 01 through 13).
In a type H exchange data set, alternative physical record
relocation is not allowed.
Type E general exchange
-----------------------
Type E exchange data sets have requirements that force the using
system to examine each field in the header label. None of these
fields can be assumed or summarized.
For type E exchange data sets, the exchange type indicator (data
set label position 44) must be an E. This means:
- On output, all supported fields must contain values that
accurately describe the data set, and all unsupported
fields must contain space characters.
- On input, all supported fields must be checked to
accurately determine the attributes of the data set.
APPENDIX G. GLOSSARY
--------------------
address:
The location of any physical record on the diskette, specified
by the cylinder number, head number, and record number. (In
publications describing the locations of a physical record on a
one-sided diskette, the address might be specified by track
number, 00, and record number.)
AM:
Address marker.
basic data exchange:
A format for exchanging data on diskettes between systems or
devices that use the IBM diskettes 1 and 2.
block
A set of adjacent logical records recorded as a unit.
blocking:
Combining two or more records into one block.
BOE:
Beginning of extent
byte:
A sequence of adjacent binary digits operated on as a unit; the
representation of one character.
C:
Celsius.
cm:
Centimeters.
cyclic redundancy check:
A method of error checking performed when reading or writing data.
cylinder:
The tracks that can be accessed without repositioning the
read/write heads.
data set:
The major unit of data storage, consisting of a collection of
data records stored in a user-specified format.
diskette drive:
The portion of the system or device that handles the diskette
functions.
diskette envelope:
The removable, protective envelope in which the diskette is
stored.
diskette jacket:
The permanent, protective cover that houses the flexible disk.
diskette magazine:
A container for up to 10 diskettes; used on the diskette
magazine drive.
diskette magazine drive:
A diskette drive that automatically loads and unloads the
diskettes from a diskette magazine.
double density:
Bits written on the IBM diskette 2D at twice the density used on
IBM diskettes 1 and 2.
drive spindle:
The portion of the diskette drive that is inserted in the
diskette and revolves, turning the disk within the jacket.
EOD:
End of data.
EOE:
End of extent.
F:
Fahrenheit.
head:
See read/write head.
ID:
Identification.
IMPL:
Initial MicroProgram Load.
index cylinder:
Cylinder 00. This cylinder is used to store information about
the diskette.
index hole:
The small hole in the disk and the jacket; used for timing.
initialization:
The process of writing the addresses, index cylinder
information, and other system information on the diskette.
(Initialization is also used to assign alternative cylinders.)
IPL:
Initial Program Load.
IRD:
Information Records Division.
kg:
Kilograms.
logical record:
A record that does not necessarily conform to the boundaries of
a physical record. The logical record can be longer than the
physical record, shorter than the physical record, or one of
several logical records within a single physical record.
permanent diskette label:
The label attached permanently to the upper left corner of the
diskette jacket.
Physical record:
One or more records written within one sector on a track.
read (operation):
The process of sensing the magnetic fields on the diskette
recording surface and converting them into signals appropriate
for use by the system or device.
read/write head:
The unit in the diskette drive that reads from or writes on the
diskette recording surface.
record:
A collection of related items of data, treated as a unit.
recording surface:
The portion of the diskette that is used to store information.
sector:
The addressable unit into which each track is divided.
spanned record:
A logical record stored in more than one block.
temporary identification label:
The removable label attached to the upper right corner of the
diskette jacket.
track:
That portion of the diskette recording surface available to one
read/write head at each access position.
type E general exchange:
A method for exchanging unformatted data on diskettes. This
exchange requires the using system to examine the header labels.
type H data exchange:
A format for exchanging data on diskettes between systems or
devices that use the IBM diskette 2D.
unblocked:
One logical record that exclusively occupies one or more blocks.
unspanned:
One or more logical records that do not extend beyond one block.
write (operation):
The process of generating magnetic fields on the diskette
recording surface.
INDEX
-----
(To be done by WS4...)
EOF